control.py

from expressions_base import Expr
from undefineds import Undefined

class IfElseStatement(Expr):
    def __init__(self, conditionals):
      self.conditionals = conditionals
      self.state = 0

    def Reset(self):
    # TODO only reset the things which we have evaled
      self.state = 0
      for hypothesis, statement in self.conditionals:
        hypothesis.Reset()
        statement.Reset()

    def Eval(self, context, sub_value):
      if sub_value and sub_value.IsTruthy():
        print "if tailcall"
        return ("tailcall", context, self.conditionals[self.state - 1][1])
      elif self.state < len(self.conditionals):
        self.state += 1
        return ("eval", context, self.conditionals[self.state - 1][0])
      return ("result", None, Undefined())

class WhileStatement(Expr):

  def __init__(self, predicate, body):
    self.pred = predicate
    self.body = body
    self.state = 0

  def Reset(self):
    self.state = 0
    self.pred.Reset()
    self.body.Reset()

  def Eval(self, context, sub_value):
    self.state = 1 - self.state
    if self.state == 1:
      self.pred.Reset()
      return ("eval", context, self.pred)
    else:
      if sub_value.IsTruthy():
        self.body.Reset()
        return ("eval", context, self.body)
      else:
        return ("result", None, Undefined())